The present invention relates to a novel series of 17,20-dihydrofusidic acid derivatives, to salts and to easily hydrolysable esters thereof, to the preparation of these compounds, to pharmaceutical compositions containing the compounds and to the use of such compounds in medicine. In particular, these compounds exhibit antimicrobial activity, thus they are useful for the treatment of infectious diseases. The compounds of the present invention can be used both in systemic treatment of infections and in topical treatment of infections related to skin and eyes.
The antibacterial properties of fusidic acid are well known. It is also known that structural variations may cause significant or total loss of such activity (cf. Godtfredsen et al, J. Med. Chem., Vol. 9, p. 15-22, 1966). It has until now been generally accepted that the double bond between the carbon atoms C-17 and C-20 which connect the side-chain to the tetracyclic ring system was essential for any antibacterial activity. Reduction of the double bond between C-24 and C-25 of fusidic acid to a single bond resulted in a marginal effect on the antibacterial activity of the molecule whereas additional reduction of the double bond between C-17 and C-20 yielding tetrahydrofusidic acid caused almost complete loss of activity. Two epimers in the series of tetrahydrofusidic acids have earlier been prepared by means of catalytic hydrogenation of fusidic acid or its isomer lumi-fusidic acid, having the configuration 17(R),20(S) and 17(R),20(R) respectively (cf. von Daehne et al., Adv. Appl. Microbiol., 25, p. 95-146,1979, and references cited therein).
The purpose of the invention is to provide semisynthetic analogues of fusidic acid having antimicrobial activity. Said purpose is achieved with the compounds of the present invention belonging to the series of dihydro- and tetrahydrofusidic acids having the essential configuration 17(S),20(S) which in vitro show high antimicrobial activity and favourable stability and pharmacokinetic properties, whereby the compounds of the invention may be used in treatment of infections in humans and animals.
The present invention provides compounds of the general formula Ia: 
wherein
Q1, Q2 and Q3 are the same or different and independently represent a xe2x80x94(CO)xe2x80x94 group; a xe2x80x94(CHOH)xe2x80x94 group; a xe2x80x94(CHOR)xe2x80x94 group; a xe2x80x94(CHSH)xe2x80x94 group; a xe2x80x94(NH)xe2x80x94 group; a xe2x80x94(CHNH2)xe2x80x94 group; or a xe2x80x94(CHNHR)xe2x80x94 group, wherein R represents an alkyl radical having 1 to 4 carbon atoms or an acyl radical having 1 to 4 carbon atoms; and wherein Q2 and Q3 may also independently represent a xe2x80x94(CH2)xe2x80x94 group;
Y represents hydrogen, hydroxy, an alkyl radical having 1 to 4 carbon atoms, or an acyl radical having 1 to 4 carbon atoms; A represents an oxygen or a sulphur atom;
R1 represents an alkyl radical having 1 to 4 carbon atoms, an olefinic group having 2 to 4 carbon atoms, a (C1-C6) acyl group, (C3-C7)cycloalkylcarbonyl group or a benzoyl group, R1 optionally being substituted with one or more halogen atoms and/or hydroxy, alkoxy or azido groups;
and pharmaceutically acceptable salts and easily hydrolysable esters thereof.
In formula Ia and subsequent formulas herein the dotted lines between C-1 and C-2 and/or C-24 and C-25 indicate that the atoms in question are connected with either a double bond or a single bond.
Preferred compounds of the invention are compounds of formula I 
wherein
Q1 and Q2 are the same or different and both represent a xe2x80x94(CHOH)xe2x80x94 group; a xe2x80x94(CO)xe2x80x94 group; or a xe2x80x94(CHSH)xe2x80x94 group;
A represents an oxygen or a sulphur atom;
R1 represents an alkyl radical having 1 to 4 carbon atoms, an olefinic group having 2 to 4 carbon atoms, a (C1-C6)acyl group, (C1-C7)cycloalkylcarbonyl group or a benzoyl group, R1 optionally being substituted with one or more halogen atoms and/or hydroxy, alkoxy or azido groups; and
pharmaceutically acceptable salts and easily hydrolysable esters thereof.
Preferably Q1 and Q2 are selected from the group consisting of xe2x80x94(CO)xe2x80x94 and xe2x80x94(CHOH)xe2x80x94. More preferred compounds of the invention are compounds of formula I wherein Q1 and Q2 both represent a 
group or one of Q1 or Q2 represents xe2x80x94(CO)xe2x80x94; A represents oxygen; R1 represents a (C1-C4)alkyl group, optionally substituted with one or more substituents selected from the group consisting of azido, hydroxy, and halogen selected from fluoro, chloro and bromo, or R1 represents an acyl group with 1 to 4 carbon atoms or a benzoyl group, both optionally substituted with one or more halogen atoms, preferably selected from the group consisting of fluoro and chloro. R1 is preferably selected from the group consisting of ethyl, 2,2,2-trifluoroethyl, 2,2,2-trichloroethyl, 2-azidoethyl, 2-hydroxyethyl, propyl and isopropyl, 1,3-difluoro-isopropyl, acetyl, propionyl, chloroacetyl and trifluoroacetyl, or R1 is selected from the preferred group consisting of ethyl, 2,2,2-trichloroethyl, 2-azidoethyl, isopropyl, tert-butyl and acetyl. Also preferred are compounds of formula I and Ia wherein the bond between C-24 and C-25 is a double bond.
Examples of compounds of the invention which can all be prepared by the methods described below are:
17(S),20(S)-Dihydrofusidic acid,
17(S),20(S),24,25-Tetrahydrofusidic acid,
11-Dehydro-17(S),20(S)-dihydrofusidic acid,
3-Dehydro-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-propionyloxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(3xe2x80x2-chloropropionyloxy)-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(2xe2x80x2-methylpropionyloxy)-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-cyclopropylcarbonyloxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-chloroacetoxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-bromoacetoxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-benzoyloxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(4xe2x80x2-fluorobenzoyloxy)-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-cyclohexylcarbonyloxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-acryloyloxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-isopropylthio-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-ethylthio-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(2xe2x80x2,2xe2x80x2,2xe2x80x2-trichloroethylthio)-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-tert-butylthio-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-methoxymethylthio-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-isopropylthio-17(S),20(S);24,25-tetrahydrofusidic acid,
16-Deacetoxy-16xcex2-acetylthio-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-benzoylthio-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-ethoxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(2xe2x80x2,2xe2x80x2,2xe2x80x2-trifluoroethoxy)-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-propoxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-isopropoxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(1xe2x80x2,3xe2x80x2-difluoroisopropoxy)-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-methoxymethoxy-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(2xe2x80x2,2xe2x80x2,2xe2x80x2-trichloroethoxy)-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(2xe2x80x2-azidoethoxy)-17(S),20(S)-dihydrofusidic acid,
16-Deacetoxy-16xcex2-(2xe2x80x2-hydroxyethoxy)-17(S),20(S)-dihydrofusidic acid,
and pharmaceutically acceptable salts and easily hydrolysable esters thereof.
In contrast to natural fusidic acid (1) wherein C-17 and C-20 are connected with a double bond, all compounds described herein and by formula I and Ia have a single bond between C-17 and C-20. The configuration of the two asymmetric carbon atoms in question is 17(S) and 20(S). This epimer is one of four possible epimers differing solely in the configuration of C-17 and C-20, and biological tests have shown this to be the only epimer exhibiting potent activity.
The compounds of the invention can be used as such or in the form of salts or easily hydrolysable esters (as hereinafter defined). The salts of the compounds are especially the pharmaceutically acceptable salts, such as alkali metal salts and alkaline earth metal salts, for example sodium, potassium, magnesium or calcium salts, as well as silver salts and salts with bases, such as ammonia or suitable non-toxic amines, such as lower alkylamines, for example triethylamine, hydroxy-lower alkylamines, for example 2-hydroxyethylamine, bis-(2-hydroxyethyl)-amine, cycloalkylamines, for example dicyclohexylamine, or benzylamines, for example N,Nxe2x80x2-dibenzylethylenediamine, and dibenzylamine. The silver salts of the compounds are especially useful for local treatment.
The expression xe2x80x9ceasily hydrolysable estersxe2x80x9d is used in this specification to denote alkanoyloxyalkyl, aralkanoyloxyalkyl, aroyloxyalkyl, for example acetoxymethyl, pivaloyloxymethyl, benzoyloxymethyl esters and the corresponding 1xe2x80x2-oxyethyl derivatives, or alkoxycarbonyloxyalkyl esters, for example methoxycarbonyloxymethyl esters and ethoxycarbonyloxymethyl esters, and the corresponding 1xe2x80x2-oxyethyl derivatives, or lactonyl esters, for example phthalidyl esters, or dialkylaminoalkyl esters, for example diethylaminoethyl esters. The expression xe2x80x9ceasily hydrolysable estersxe2x80x9d includes in vivo hydrolysable esters of the compounds of the invention. Such esters may be prepared using methods known to a skilled person in the art, cf. GB patent No. 1 490 852 hereby incorporated by reference.
As used in the specification, unless specified to the contrary, the following terms have the meanings indicated, cf. also IUPAC Recommendations 1994 http://www.chem.qmw.ac.uk/iupac/class/.
xe2x80x9cAlkylxe2x80x9d refers to any univalent group derived from an alkane by removal of a hydrogen atom from any carbon atom, and includes the subclasses of normal alkyl (n-alkyl), and primary, secondary and tertiary alkyl groups respectively, and having the number of carbon atoms specified, including for example (C1-C4)alkyl, (C1-C3)alkyl, (C1-C2)alkyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and t-butyl. Alkane refers to an acyclic branched or unbranched hydrocarbon having the general formula CnH2n+2, where n represents an integer, and therefore consisting entirely of hydrogen atoms and saturated carbon atoms.
xe2x80x9cOlefinic groupxe2x80x9d refers to a straight or branched acyclic hydrocarbon having one or more carbon-carbon double bonds of either E or Z stereochemistry where applicable, and having the number of carbon atoms specified. The term includes, for example, (C2-C4)olefinic group, preferably a (C2-C4)alkenyl; (C2-C3)olefinic group, preferably a (C2-C3)alkenyl; vinyl; allyl; 1-butenyl; 2-butenyl; and 2-methyl-2-propenyl. Further, xe2x80x9colefinic groupxe2x80x9d refers to a straight or branched alkynyl moiety having at least one triple bond. This term would include, for example, crotyl and propargyl. Olefinic groups having only one carbon-carbon double bond, herein called alkenyl, are preferred.
xe2x80x9cArylxe2x80x9d refers to groups derived from monocyclic and polycyclic aromatic hydrocarbons by removal of a hydrogen atom from a ring carbon atom, e.g. o-tolyl, phenyl, naphthyl. The number of carbon atom in an aryl group is typically 6, 7, 8, 9 or 10.
xe2x80x9cAcylxe2x80x9d refers broadly to a radical of the formula Rxe2x80x94COxe2x80x94, where R is alkyl as defined above, for example (C1-C6)acyl.
xe2x80x9cAlkoxyxe2x80x9d refers broadly to a radical of the formula xe2x80x94OR, where R is alkyl as defined above, for example (C1-C5)alkoxy, (C1-C3)alkoxy, methoxy, n-propoxy, t-butoxy, and the like.
xe2x80x9cHalogenxe2x80x9d means the same or different of fluoro, chloro, bromo, and iodo; fluoro, chloro, and bromo being more useful in the present compounds.
xe2x80x9cAlkanoylxe2x80x9d refers broadly to a radical of the formula xe2x80x94Rxe2x80x94COxe2x80x94, where R is alkyl as defined above, for example (C1-C8)alkanoyl, acetyl, propionyl, isopropionyl, butyryl. xe2x80x9cAralkanoylxe2x80x9d refers broadly to a radical of the formula xe2x80x94R(CH2)nxe2x80x94COxe2x80x94, wherein R is aryl as defined above and n is an integer, preferably selected from 1, 2, 3, and 4. xe2x80x9cAroylxe2x80x9d refers broadly to Rxe2x80x94COxe2x80x94 where R is an aryl group as defined above.
xe2x80x9cAlkanoyloxyalkylxe2x80x9d or xe2x80x9caroyloxyalkylxe2x80x9d refer broadly to a radical of the formula xe2x80x94CH2xe2x80x94Oxe2x80x94COxe2x80x94R, wherein R represents a (C1-C6)alkyl group or a (C6-C8)aryl group. Aryl and alkyl are as defined above.
xe2x80x9cAlkoxycarbonyl-xe2x80x9d and xe2x80x9caryloxycarbonyl-xe2x80x9d refer to the group xe2x80x94COxe2x80x94OR or xe2x80x9cacyloxy-xe2x80x9d refers to the group Rxe2x80x94COxe2x80x94Oxe2x80x94 wherein R is alkyl or aryl as defined above.
There are several chiral centres in the compounds according to the invention because of the presence of asymmetric carbon atoms. The presence of several asymmetric carbon atoms gives rise to a number of stereoisomers with R or S configuration at each chiral centre. General formula I and Ia, and (unless specified otherwise) all other formulae in this specification are to be understood to include all such stereoisomers in pure form and as mixtures (for example stereoisomeric mixtures) except where the configuration is expressly indicated.
In the compounds of formula I and Ia, the preferred stereochemistry is in general as follows: when Q1 and Q2 refer to the 
group the configuration at C-3 and C-11 in the compounds of formula I and Ia is 3xcex1 and 11xcex1, respectively. The C-16 atom carrying the A group has the (S)-configuration, hereinafter denoted 16xcex2. In the formulas herein plain lines depict bonds approximately in the plane of the drawing; bonds to atoms above the plane are shown with a bold wedge starting from an atom in the plane of the drawing at the narrow end of the wedge; and bonds to atoms below the plane are shown with short parallel (wedged) lines. Substituents above the plane are described as xcex2 and shown as a bold wedge, those below the plane are described as xcex1 and shown by a line with short parallel (wedged) lines.
Biological Activity
In vitro investigations have evidenced high potency of compounds of the invention against several bacteria including staphylococci, streptococci, corynebacteriae and mycobacteriae. Biological tests have revealed comparable antibacterial activity of 17(S),20(S)-dihydrofusidic acid (10) (Compound 101) to that of fusidic acid (1) as can be seen from Table 1 showing MIC values of the two mentioned compounds towards a number of bacteria. The biological tests are conducted on microtitter plates using liquid medium containing broth.
Also other compounds of the invention exhibit high in vitro activity against several bacteria. The antibacterial activity of some of these compounds relative to fusidic acid appears from Table 2 showing MIC values for compounds of the invention. The method used is recommended by the European Pharmacopoeia 3rd Ed. (1997) for testing the potency of antibiotics. It is an agar diffusion method where the same volume of the tested solution is added to cavities in agar. The inhibition zones are a function of the concentration of the fusidic acid analogue used. All assays are run with fusidic acid (1) as the reference substance. The results in Table 2 differ from those of Table 1 due to the different experimental methods used.
Furthermore, compounds of the invention possess several advantages compared to the corresponding compounds containing the 17,20 double bond, such as fusidic acid:
The compounds of formula I and Ia are chemically more stable, possibly due to the lower acidity of the saturated 17,20 bond and the absence of conjugation of the carboxylic acid with a carbon-carbon double bond.
The compounds of formula I and Ia are less easily degraded when exposed to sunlight.
The compounds of formula I and Ia are more stable in solution: A solution of the compound of formula 10 shown below in ethanol stored at 0xc2x0 C. for 1 month retained  greater than 80% of initial activity whereas a corresponding solution of fusidic acid retained only about 70% of initial activity.
The compounds of formula I and Ia are more lipophilic and thus more suitable for topical preparations.
Being semi-synthetic the compounds of formula I may be prepared from a relatively crude fusidic acid raw material which is otherwise not suitable for medicinal purposes.
The following standard abbreviations are used throughout this disclosure:
AcOH=acetic acid
Ac2O=acetic anhydride
Ac=acetyl
Bu=n-butyl
tBu, tBu=tert-butyl
Et=ethyl
Ether=diethyl ether
Me=methyl
MOM=methoxymethyl
MOMO=methoxymethyl-O
Ph=phenyl
TBAF=tetra-n-butylammonium fluoride
TBS=tert.butyl dimethylsilyl
TBSCl=tert.butyl dimethylsilyl chloride
THF=tetrahydrofuran
TLC=Thin Layer Chromatography
TMS=trimethylsilyl
Preparations of Compounds of the Invention
17S,20S-Dihydrofusidic acid (10) may be prepared starting from naturally occurring fusidic acid by the sequence outlined in Scheme 1 below: Fusidic acid (1) is first converted into lactone (2) by deacetylation followed by acidification. The double bond between C-17 and C-20 in (2) is reduced with NaBH4 in aqueous methanol with cis attack from the xcex1-face of the molecule yielding lactone (3). Inversion at C-20 is obtained quantitatively by heating lactone (3) in the presence of 28% aqueous sodium hydroxide. The hydroxy groups at C-3 and C-11 in lactone (4) are subsequently protected as methoxymethyl (MOM) ethers. Reduction of the protected lactone (5) with LiAlH4 yields diol (6) which is first protected selectively at the primary hydroxy group at C-21 with a diphenylmethylsilyl group followed by acetylation of the hydroxy group at C-16. After desilylation of (7) using tetrabutylammonium fluoride (TBA+Fxe2x88x92) buffered with acetic acid, the free hydroxy group in (8) can be oxidised, first to the aldehyde by Dess-Martin periodinane and further to the carboxylic acid (9) by sodium chlorite. Compound (10) is obtained in a final step by cleavage of the MOM groups in (9) by treating with trimethylsilyl bromide (TMSBr) in anhydrous dichloromethane.
The compound of formula 10 is a compound of the invention (Compound 101) and further a general starting compound for analogues corresponding to formula I as hereinafter described. 
Compound 101 may alternatively be prepared employing a TBS protective group for masking of the 3-hydroxy function in compound 4 leaving the 11-hydroxy group unprotected. The TBS protected compound 11 (Scheme 2) is then reacted in corresponding manner to that shown in Scheme 1. Final cleavage of the TBS group is achieved by treating compound 16 with diluted hydrofluoric acid yielding the compound of formula 10 (Compound 101). 
The compounds of general formula I may be prepared by a method comprising a first step in which compounds of the general formula II is converted into 16-bromo compounds of formula III as described below. 
in which formulas Q1xe2x80x2 and Q2xe2x80x2 represent a xe2x80x94(CO)xe2x80x94 group, 
R3 representing a common protective group such as alkanoyl, aralkanoyl, alkanoyloxyalkyl or aroyl, or a trisubstituted silyl radical substituted with alkyl, oxyalkyl, aryl or oxyaryl groups; R2 is a straight or a branched alkyl radical having from 1-6 carbon atoms, e.g. methyl, ethyl, tert-butyl, an unsubstituted or substituted aralkyl radical, e.g. benzyl, nitrobenzyl, an alkanoylmethyl or aroylmethyl radical, e.g. acetonyl or phenacyl, an alkanoyloxyalkyl, or aroyloxyalkyl radical, e.g. acetoxymethyl, pivaloyloxymethyl or benzoyloxymethyl, an alkoxymethyl radical or a cyanomethyl radical, a silyl radical substituted with groups of alkyl, alkenyl, oxyalkyl, oxyalkenyl, aryl or oxyaryl, e.g. triethylsilyl, triisopropylsilyl, diphenylmethylsilyl, tert-butyldimethylsilyl, tert-butyldiphenylsilyl, tert-butoxydiphenylsilyl; the dotted line between C-24 and C-25 has the meaning as defined above.
The conversion is performed by reacting a compound of formula II with tetrabromomethane/triphenylphosphine or with N,N-dimethylformimidate bromide in an inert solvent, e.g. ether, tetrahydrofuran or dimethylformamide, and at or below room temperature (cf. von Daehne, W. and Rasmussen, P., 1975, GB Patent No. 1 523 803).
Compounds of formula II are prepared starting from compounds in Scheme 1 by methods known from the literature (cf. GB Patent No. 1 490 852 and GB Patent No. 1 523 803) or by analogous methods. Starting compounds of formula III can for instance be prepared from the compound of formula 10 or more conveniently from the compound of formula 9 as outlined in Scheme 3. 
In a next step intermediates of formula III are reacted with compounds of formula IV to form, with inversion of configuration at C-16, compounds of formula V: 
in which formulae Q1xe2x80x2, Q2xe2x80x2, A, R1, R2 and the dotted line between C-24 and C-25 have the meanings defined above. The conversions are performed according to procedures known from the literature (cf. von Daehne, W. and Rasmussen, P., 1975, GB Patent No. 1 523 803). When A in formula V represents oxygen and R1 is different from acyl, the reacting compounds of formula IV are preferably used as solvents and the reaction is performed in the presence of a silver or mercury salt, e.g. silver carbonate, silver trifluoroacetate or mercury acetate, or a base, e.g. potassium carbonate, sodium bicarbonate or sodium (C1-C5)alcoholate, preferably sodium methanolate or sodium ethanolate, and at room temperature or slightly elevated temperature. If A in formula V represents sulphur and R1 is different from acyl, the reaction is performed in an inert organic solvent, preferably ethanol or dimethylformamide, in the presence of a base, e.g. potassium hydroxide or sodium hydride, and at or below room temperature or slightly elevated temperature.
When A in formula V represents oxygen and R1 represents acyl, the reaction is carried out with the corresponding silver salts of the compounds of formula IV in an inert solvent, e.g. benzene, and at room temperature or slightly elevated temperature. When A in formula V represents sulphur and R1 represents acyl, the reacting compounds of formula IV are preferably used as their potassium or sodium salts and the reaction is performed in an inert solvent, e.g. dimethylformamide, and at room temperature.
The compounds of formula V, wherein A represents oxygen and R1 represents a (C1-C6)acyl group or a benzoyl group, can be prepared from the compounds of formula II by reaction with a reactive derivative of the carboxylic acids of formula IV, e.g. an acid chloride or acid anhydride. The reaction is performed in the presence of a base, preferably pyridine, in an inert solvent, e.g. dimethylformamide or pyridine, and at or below room temperature.
In a final step the compounds of formula V can be converted into the compounds of formula I by hydrolysis, either in the presence of a base such as sodium or potassium hydroxide or carbonate in aqueous methanol or ethanol, or in the presence of an acid such as hydrochloric acid or p-toluenesulphonic acid in aqueous tetrahydrofuran, depending on the nature of Q1xe2x80x2, Q2xe2x80x2, R1 and R2.
Compounds of formula V in which Q1xe2x80x2, Q2xe2x80x2 represent the group 
or xe2x80x94(CO)xe2x80x94 and R2 represents an easily hydrolysable ester radical are without further conversion compounds of the invention.
Compounds of formula V in which Qxe2x80x21 and/or Qxe2x80x22 represent the group 
or xe2x80x94(CO)xe2x80x94, and R3 represents an alkanoyl, alkoxyalkyl, aralkanoyl or aroyl radical can be converted to compounds of the invention by hydrolysis in aqueous methanol, ethanol or THF in presence of an acid such as hydrochloric acid, acetic acid and p-toluenesulphonic acid or in anhydrous non-protic organic solvents, e.g. dichloromethane in presence of a Lewis acid, e.g. trimethylsilyl bromide. If R3 represents an alkoxy or an aryloxy radical, compounds of formula V can be converted to compounds of the invention by hydrolysis in aqueous methanol or ethanol and in the presence of a base such as sodium or potassium hydroxide or carbonate.
The compounds of formula V in which Q1xe2x80x2, Q2xe2x80x2 each represent the group 
or xe2x80x94(CO)xe2x80x94 and R2 represents an unsubstituted or substituted benzyl radical, a cyanomethyl, alkanoylmethyl or aroylmethyl can also be converted into compounds of formula I by reduction. In the case where R2 represents a benzyl or a cyanomethyl radical, catalytic hydrogenation is preferred, whereas, when R2 represents acetonyl, phenacyl or trichloroethyl radical, a reduction with zinc in acetic acid can be used. When R2 is a substituted silyl radical, acid hydrolysis using diluted acids such as hydrochloric acid, acetic acid or toluenesulphonic acid or fluoride assisted cleavage, e.g. hydrogen fluoride in acetonitrile or tetrabutylammonium fluoride in THF can be used.
The compounds of general formula I in which A represents an oxygen may alternatively be prepared by a method comprising a first step in which compounds of the general formula VI are converted into 16-acyloxy or 16-O-alkyl compounds of formula VII as described below: 
in which formulas Q1xe2x80x2, Q2xe2x80x2, R1 and the dotted line between C-24 and C-25 have the meanings defined above; and R4 represents a common protective group such as alkanoyl, aralkanoyl, alkanoyloxyalkyl or aroyl, or a trisubstituted silyl radical substituted with alkyl, oxyalkyl, aryl or oxyaryl groups.
R4 is preferably a silyl protective group such as diphenylmethylsilyl or tert.butoxydiphenylsilyl, or an acyl protective group such as acetyl or pivaloyl.
For compounds of formula VII in which R1 represents an alkyl radical as defined above, the conversion is performed by reacting a compound of formula VI with an alkylhalide or an alkyltriflate according to general methods of ether preparations known to those skilled in the art. For compounds of formula VII in which R1 represents an acyl group, the conversion is performed by reacting a compound of formula VI with an acylchloride or a corresponding acid anhydrides in presence of a weak base according to general acylation methods known to those skilled in the art. Compounds of formula VII can be converted to compounds of formula I by first removing the R4 protective group by known methods and then by the same reaction steps f and g as described in Scheme 2 or by related methods.
The compounds of formula I wherein Q1 and/or Q2 represent xe2x80x94(CO)xe2x80x94 can also be prepared from the corresponding compounds of formula I wherein Q1 and Q2 both represent the group 
by oxidation methods known by those skilled in the art.
The invention further relates to a method for producing a compound of formula I wherein the inversion of C-20 is obtained quantitatively by heating the lactone of formula 3 herein in the presence of concentrated sodium hydroxide.
The easily hydrolysable esters of the compounds of formula I and Ia can be prepared in known manner by methods described in the literature.
Compounds of the invention in which C-24 and C-25 are connected by a single bond can be prepared from the corresponding unsaturated analogues by reduction, e.g. by catalytic hydrogenation using catalysts such as palladium or platinum. Compounds such as helvolic acid and cephalosporin P1 may be used as starting materials in the preparation of other compounds of general formula Ia.
Compounds of formula II are prepared starting from compounds in Scheme 1 by methods known from the literature (cf. GB Patent No. 1 490 852 and GB Patent No. 1 523 803) or by analogous methods. Starting compounds of formula III can for instance be prepared from the compound of formula 10 or more conveniently from the compound of formula 9 as outlined in Scheme 3.
It is a further object of the present invention to provide pharmaceutical compositions which are useful in the treatment of infectious diseases in the human and veterinary practice.
With this object in view, the composition of the invention contain as an active component at least one member selected from the group consisting of compounds of formula Ia and formula I (hereinafter referred to as the active ingredient) including acceptable salts and easily hydrolysable esters thereof together with acceptable pharmaceutical carriers and/or diluents.
In said composition, the proportion of therapeutically active material to carrier substance can vary from 0.5% to 95% by weight. The compositions can be worked up to various pharmaceutical forms of presentation such as granulates, tablets, pills, dragees, suppositories, capsules, sustained-release tablets, suspensions, injection and may be filled in bottles or tubes or similar containers. Pharmaceutical organic or inorganic, solid or liquid carriers and/or diluents suitable for oral, enteral, parenteral or topical administration can be used to make up compositions containing the present compounds: Water, gelatine, lactose, starch, magnesium stearate, talc, vegetable and animal oils and fats, benzyl alcohol, gum, polyalkylene glycol, petroleum jelly, cocoa butter, lanolin, and other emulsifying agents, salts for varying the osmotic pressure or buffers for securing an appropriate pH-value of the composition can be used as auxiliary agents.
Furthermore, the composition may contain other therapeutically active components which can appropriately be administered together with the compounds of the invention in the treatment of infectious diseases such as other suitable antibiotics, in particular such antibiotics which may enhance the activity and/or prevent development of resistance. Such antibiotics include penicillins, cephalosporins, tetracyclines, rifamycins, erythromycins, lincomycin, clindamycin and fluoroquinolones. Other compounds which advantageously may be combined with the compounds of the invention, especially in topical preparations, include e.g. corticosteroids, such as hydrocortisone or triamcinolone. Alternatively, such other therapeutically active component(s) may be administered concomitantly (either simultaneously or sequentially) with the composition of the invention.
For granulates, tablets, capsules or dragees the pharmaceutical composition of the invention appropriately contains from 25% to 98% of the active substance of the invention, and in oral suspensions the corresponding amount is appropriately from 2% to 20% active ingredient.
When the compounds are administered in the form of salts with pharmaceutically acceptable non-toxic bases. The preferred salts are for instance easily water-soluble or slightly soluble in water, in order to obtain a particular and appropriate rate of absorption.
As indicated above, the compounds of formula I and Ia and their salts may be worked up to pharmaceutical forms of presentation including suspensions, ointments and creams: A pharmaceutical preparation for oral treatment may also be in form of a suspension of the active ingredient as such or in the form of a sparingly water-soluble pharmaceutically acceptable salt, the preparation containing from 20 to 100 mg per ml of vehicle. A pharmaceutical preparation for topical treatment may be in the form of an ointment or cream containing the active ingredient in an amount of from 0.5 to 50% of preparation. Topical preparations are favourable due to the stability towards sunlight and the relatively lipophilic nature of the present compounds.
Another object of the invention resides in the selection of a dose of the compounds of the invention which dose can be administered so that the desired activity is achieved without simultaneous secondary effects. In the human systemic therapy the compounds and their salts are conveniently administered (to adults) in dosage units containing no less than 50 mg and up to 1000 mg, preferably from 200 to 750 mg, calculated as the compound of formula I.
By the term xe2x80x9cdosage unitxe2x80x9d is meant a unitary, i.e. a single dose which is capable of being administered to a patient, and which may be readily handled and packed, remaining as a physically and chemically stable unit dose comprising either the active material as such or a mixture of it with solid or, liquid pharmaceutical diluents or carriers.
In the form of a dosage unit, the compound may be administered one or more times a day at appropriate intervals, always depending, however, on the conditions of the patient, and in accordance with the prescription made by the medical practitioner.
Thus in systemic treatment a daily dosage will preferably be an amount of from 0.5 to 3 g of the active ingredient.
The term xe2x80x9cusage unitxe2x80x9d in connection with topical use means a unitary, i.e. a single dose capable of being administered topically to a patient in an application per square centimeter of the infected area of from 0.1 mg to 10 mg and preferably from 0.2 mg to 1 mg of the active ingredient in question.
If the composition is to be injected, a sealed ampoule, a vial or a similar container may be provided containing a parenterally acceptable aqueous or oily injectable solution or dispersion of the active ingredient as the dosage unit.
The parenteral preparations are in particular useful in the treatment of conditions in which a quick response to the treatment is desirable. In the continuous therapy of patients suffering from infectious diseases, the tablets or capsules may be the appropriate form of pharmaceutical preparation owing to the prolonged effect obtained when the drug is given orally, in particular in the form of sustained-release tablets.
In the treatment of infectious diseases, such tablets may advantageously contain other active components as mentioned herein before.
Still another object of the invention is to provide a method of treating patients suffering from infectious diseases, the method comprising administering to patients from 0.03 g to 0.7 g/kg body weight per day in 1 to 3 doses, preferably from 0.5 g to 3 g per day of a compound of formula I or Ia or an equivalent amount of a salt as defined before of a compound of formula I or Ia. Preferably, the active ingredient is given in the form of the dosage units as before said.
The invention will be further described in the following non-limiting Preparations and Examples.